Generally, the hard disk drive (HDD) includes the suspension substrate provided with a magnetic-head slider adapted for writing and reading data relative to a disk for storing the data therein. This suspension substrate includes a spring metal layer and a plurality of (e.g., four to six) wirings, respectively layered on the spring metal layer, via an insulating layer. With this configuration, when an electric signal is transmitted through each wiring, the writing or reading of the data can be performed relative to the disk.
In recent years, there has been a demand for accelerating a transmission line, in order to increase the amount and speed of data processing. To this end, it is necessary to enhance the electric properties, such as impedance and the like, of the substrate.
For instance, in order to reduce the impedance, it is effective to narrow the space or gap between each pair of differential wirings. In this case, however, there is a risk that a short circuit may tend to occur between such a pair of differential wirings.
To address this problem, various suspension substrates have been proposed.